The work proposed for this component of the Center grant is oriented to development of implantable strains of oral bacteria, particularly Streptococcus sanguis, that will be able to moderate the cariogenicity of plaque. The general plan is to produce bacteria with enhanced capacities to produce ammonia from arginine or arginine-containing peptides. The bacteria should be constitutive producers of ammonia with altered catabolite repression. They must be able to compete with wild strains in plaque and to become established as long-term members of the flora. Recent studies by Hillman et al. (J. Dent. Res. 66:1092, 1987) and by others indicate that laboratory-grown bacteria can be introduced into the plaque community, and their survival depends on how well they compete with the resident bacteria. Therefore, the proposed studies include not only genetic manipulation of bacteria strains and attempts at implantation, but also a thorough examination of the physiological aspects of the arginine deiminase system and selection of competitive strains through mixed culture in vitro plaque. The specific aims of the project are: 1. Genetic characterization of the arginine deiminase system of Streptococcus sanguis and related organisms with respect to numbers of genes, chromosomal ordering of genes and regulatory elements. 2. Physiological characterization of the system with emphasis on enzymology, regulation and the roles of the system in the overall workings of the cell. 3. Transfer of genes for the arginine deiminase system to Streptococcus mutans and conversion of S. mutans to an arginine-positive organism. 4. Production of stable arginine-deiminase-negative mutants of Streptococcus rattus for evaluation of the role of the system in cariogenicity for rodents. 5. Production of strains of S. sanguis with enhanced capacities to produce ammonia from arginine or arginine-containing peptides. The strains will be grown in mixed, in vitro plaque with other bacteria to improve their capacities to compete in plaque and will then be used to implant rodents.